boat slowing down

Ron Hill · July 16, 2015, 02:33:27 PM

Rick : Sounds to me like you need to re-plumb the fuel line coming out of the fuel tank!!

Should be : Fuel tank to primary filter (Racor/Dahl) then to the electric fuel pump and then to the engine fuel pump!! (not tank to pump to filter!!)

Then there is no need to ever check the screen in the electric pump as it receives filtered fuel!!

A thought

Bobg · October 06, 2015, 08:12:49 AM

bringing up a old post, my boat is still slowing down, I have checked the rpm with a hand held, the rpm's do registrar a couple hundred low, but all that being said, at 2200 on hand held, the boat can only get about 4.3 knots, I checked the prop shaft, it is registering 1100 rpm. I heard that it should be about half. or 2-1 ratio. The boat is empty of stuff, tanks empty except fuel, no dinghy, 2 people. I used to get about 5.7 knots on a regular basis. new filters installed.
Ron I haven't tried turning the shaft while in gear yet. can't seem to find where it says how check transmission in the wiki. lots of other stuff, but that. tranny fluid changed this spring looks good
I do see where the injection pump was the cause for one owner, looks like a pain to remove, do all the electric fuel pumps have a mystery filter? or screen.
under power I can get 3000 rpm, at dock out of gear, it will quickly get 3200 rpm,
I have 1000 hours on engine, any more ideas?, thanks guys. pulling boat this week for winter

patrice · October 06, 2015, 08:32:43 AM

Quote from: Bobg on October 06, 2015, 08:12:49 AM
bringing up a old post, my boat is still slowing down, I have checked the rpm with a hand held, the rpm's do registrar a couple hundred low, but all that being said, at 2200 on hand held, the boat can only get about 4.3 knots, I checked the prop shaft, it is registering 1100 rpm. I heard that it should be about half. or 2-1 ratio. The boat is empty of stuff, tanks empty except fuel, no dinghy, 2 people. I used to get about 5.7 knots on a regular basis. new filters installed.
Ron I haven't tried turning the shaft while in gear yet. can't seem to find where it says how check transmission in the wiki. lots of other stuff, but that. tranny fluid changed this spring looks good
I do see where the injection pump was the cause for one owner, looks like a pain to remove, do all the electric fuel pumps have a mystery filter? or screen.
under power I can get 3000 rpm, at dock out of gear, it will quickly get 3200 rpm,
I have 1000 hours on engine, any more ideas?, thanks guys. pulling boat this week for winter

Hi Could it be in your boat's NAME the issue ???

If the engine is running at same speed it was before and you used to get higher speed, then the trouble should be between engine and prop.
Like mentioned by .... with engine NOT running, if you put in gear, is the prop shaft locked ? can you turn by hand.
Or you will be able to check prop when out of water.

Good luck

Ron Hill · October 07, 2015, 02:22:11 PM

Bob : All pumps have a screen installed by the manufacturer to protect the pump!!

patrice · October 09, 2015, 05:44:38 AM

Hi bob,

I don't think your issue is from a bad filter or something else with engine.
If the engine run at same RPM as before, and can keep it, then these option should be ruled out.

Now, it should be between the engine and the prop.
Imagine your car engine running at 2500 rpm and going at 60mph on the road, next day engine running at 2500rpm but doing 30mph. Are you checking the engine or something else?

In your case, it is a good chance that transmission is slipping, or that your prop got damaged by a debris in water. It does not take much for the prop to cavitate if not perfect.
Or I'm going for a long shot, but when you got the prop repitch, did you had good result after, or the issue is since that. Could be a not perfect repitch ??

I'm not an expert, but trying to find things to look for....

Jack Hutteball · October 09, 2015, 07:59:34 PM

When we bought our MK ll in 2001, within the first year the boat would slow sometimes. I could see the shaft slow while watching it with the engine running at constant RPM. Dealer insisted it was shift connection on the transmission and adjusted it several times. Problem not solved. Transmission was removed from the boat twice and checked in a shop, who could find no problems with it. Seemed to work on the workbench. Put it back in the boat, still the same problem. Long and short of it, Catalina replaced the transmission. No more problems 14 years later.

Maybe a similar problem with your transmission?

Jack
C34 MK ll 2001, FK/TR M35BC

Bobg · October 12, 2015, 06:22:53 AM

When I had the prop repitched from 9 to 10, my boat speed increased to around 5.8 knots, up from the usual 5.5 so it did help somewhat, Pulled the boat for the winter, had a friend try to turn the prop by hand while I secured the engine from turning over. he couldn't turn the prop while in gear,, if I didn't stop the engine from turning over he could turn the prop and the engine would turn also. Also when in the water, the transmission would turn at 50% engine speed, i.e., 2000 rpm on engine, 1000 rpm on transmission, all test seem to favor the fact the transmission is probably ok.. next time on the boat I am going to give the engine a compression test. and reflect all winter on what it is.

KWKloeber · October 12, 2015, 06:44:42 AM

Quote from: Bobg on October 12, 2015, 06:22:53 AM
When I had the prop repitched from 9 to 10, my boat speed increased to around 5.8 knots, up from the usual 5.5 so it did help somewhat, Pulled the boat for the winter, had a friend try to turn the prop by hand while I secured the engine from turning over. he couldn't turn the prop while in gear,, if I didn't stop the engine from turning over he could turn the prop and the engine would turn also. Also when in the water, the transmission would turn at 50% engine speed, i.e., 2000 rpm on engine, 1000 rpm on transmission, all test seem to favor the fact the transmission is probably ok.. next time on the boat I am going to give the engine a compression test. and reflect all winter on what it is.

Bob,
What's your rationale for a compression test?
From your info, the engine turns at near the correct RPM, the shaft turns at near the correct RPM.
There's no RPM issue based on your data.

If the shaft is turning at the correct speed, logic says the issue is behind the transmission -- ie, a prop issue or a hull issue, or are motoring through molasses.

kk